1. Field of the Invention
This invention relates to a resin composition containing fine silica particles having good dispersibility therein and which retains the desirable properties of light transmission, selective absorption, refraction, reflection, scattering, light emission and lighting control of the resin composition.
2. Description of the Prior Art
Synthetic resin containing fine particles of silica or glass dispersed therein are widely used, as described for example in Japanese Patent Application Kokai (Laid-Open) No. 5742/82, as materials for lighting fixtures or screens by virtue of their light diffusion property. These materials have generally been prepared either by a method which comprises dispersing fine particles of silica or glass into a transparent resin such as methacrylic or styrene resin and then forming the composition thus obtained into articles, or by a method which comprises dispersing the fine particles into monomers or a partially polymerized monomer (syrup) and then polymerizing the resulting composition to form a solid material. However, these methods have difficulties, since fine particles of silica or glass have higher specific gravities than the monomer or syrup. As a result, the particles are liable to sediment or aggregate during the polymerization or can be hardly dispersed uniformly in the resin when kneaded with resin.
Accordingly, a process has been proposed by the present inventors which comprises, in producing a light diffusive methacrylic resin sheet by mixing SiO.sub.2 into methacrylic resin, first preparing a part of a syrup, mixing SiO.sub.2 therewith to form so-called color master batch, and then mixing the master batch with the remainder of the syrup [Japanese Patent Application Kokai (Laid-Open) No. 16,007/82]. However, this process has disadvantages in that it involves increased number of process steps and yet the dispersion of the SiO.sub.2 cannot be deemed to be perfect.